Histological and clinical studies on the effects of low to medium level infrared light therapy on human and mouse skin

Journal of Drugs in Dermatology, March, 2008 by Koichiro Kameyama

Introduction

Phototherapy of the skin has been used for many years, but its exact mechanism of action is still not clear. (1) Nonablative laser or intense pulsed light (IPL) therapies have been reported to require thermal damage of the dermis. (2,3) Thermal damage denatures the collagen, and the remodeling of collagen encourages the generation of collagen and results in tighter skin. The wavelengths used have ranged from approximately 500 to 1800 nm. The target chromophores for nonablative skin rejuvenation are melanin, hemoglobin, and water. Each molecule of hemoglobin carries 4 heme groups; the heme gives hemoglobin (and blood) its red color. (4) Cytochromes constitute a family of colored proteins, and each cytochrome contains 1 or more heme groups. Cytochromes play important roles in the electron-transport chain in mitochondria, (5) suggesting that mitochondria can be a target chromophore during skin rejuvenation as well as hemoglobin. Helium-neon laser light (1-10 mW) can penetrate as far as 0.5 mm into freshly excised human skin and delivers the highest relative percentage of incident energy to a certain volume of tissue. (6) With longer wavelengths emitted by infrared lasers, the depth of penetration has been shown to be even greater, reaching several millimeters. (7) A penetration depth of a few microns can be regarded as sufficient because most of the relevant target cells of low level laser irradiation, namely fibroblasts, keratinocytes, macrophages and endothelial cells, are located within the epidermis and upper dermis. (6)

Each cell contains a number of power plants called mitochondria. Mitochondria exist in all kinds of human cells except red blood cells. The function of those power plants is to produce adenosine triphosphate (ATP), a form of energy required for cell function. (6) The main function of ATP is to provide energy for 3 major processes: membrane transport, muscle contraction, and synthesis of proteins (8) (ie, collagen and elastin). Low level laser light reaches the mitochondria of cells in the tissue where the photonic energy is absorbed by the collector surfaces. There, it is converted to chemical energy (9) within the cell in the form of ATP as an additional source of energy. Mitochondria produce more ATP, which leads to normalization of cell functions, pain relief, and healing. (9,10)

Low level laser irradiation (LLLI) is a nonthermal irradiation within the visible to near infrared range of the light spectrum. Low level laser irradiation has been reported to stimulate the proliferation of various kinds of cells, including fibroblasts, endothelial cells, and keratinocytes, and to augment collagen synthesis in fibroblasts. (11-13) In vitro, LLLI stimulates proliferation and collagen synthesis and modulates matrix metalloproteinase activity and gene expression in porcine aortic smooth muscle cells. (14) Although deep heating or thermal damage has been reported to be necessary for skin rejuvenation, those reports suggest that visible to near infrared low level ranges of light can cause histological changes and elicit clinical improvement by activating mitochondria in vivo. Melanin is the target chromophore for visible to near infrared light. (2) Therefore, water, mitochondria and hemoglobin can absorb many photons of visible to infrared light in the absence of melanin. If mitochondria are target chromophores for phototherapy in vivo, histological changes would be expected to be more remarkable in amelanotic mouse skin compared to pigmented human skin, since melanin absorbs many photons and avoids photon-induced mitochondria activation.

Materials and Methods

The subject was a 51-year-old Japanese male. The skin was treated with infrared light generated using a Titan [R] source (Cutera, Brisbane, CA) with a 1.0 x 3.0cm hand piece. The spectrum of the Titan is from 1100 to 1800 nm, including the filtering of strongly absorbing wavelengths in the 1400-nm to 1500-nm range. Skin tissue biopsies from the thigh where taken before any irradiation (control). Infrared light of 10, 20, or 30 J/[cm.sup.2] was irradiated on the subject's skin on days 0, 2, 4, and 7 and biopsies were taken on day 11. Four passes of irradiation with the Titan were performed at each treatment day.

[FIGURE 1 OMITTED]

Amelanotic (BALB/cAJcl-nu/nu) mice were purchased from Nihon Kurea (Tokyo, Japan). Skin tissues biopsies were again taken before before treatment (control). At each treatment, 4 passes of 5, 10, 20, or 30 J/[cm.sup.2] Titan infrared were used to irradiate 4-week-old amelanotic mouse skin on days 0 and 3. Skin tissue biopsies were taken on day 7.

Results

Human skin

Biopsies from the subject skin tissue demonstrated that the all 10, 20, and 30 J/[cm.sup.2] infrared treatments increased the amounts of collagen compared to the untreated control (Figure 1). Each collagen bundle became thicker when compared to the untreated controls. Irregularly shaped denatured collagen was observed in the mid dermis of skin when irradiated at 30 J/[cm.sup.2] (Figure 2). Irregularly shaped nuclei or nuclear debris were observed around the denatured collagen. The amount of elastin was increased in a dose-dependent manner. Relatively thin elastin was distributed between the collagen in 10 and 20 J/[cm.sup.2] irradiated skin; however random-coiled shape elastins were observed in 30 J/[cm.sup.2] irradiated skin (Figure 3). The thickness of the epidermis was not changed significantly.